People have had Yellow Tangs for a long time without them getting huge.
@outerbank has a 26 or 27-year old Yellow Tang and it’s about 5” or so.
@CanuckReefer has an 18-year old one and it’s probably about 5” as well.
A South African guy with a 1750 gallon tank has had some Yellow Tangs for 20+ years or so and they got to maybe 5-5.5”.
So I don’t think many exceed 5.5-6” if started small.
However I’d still give them at least a 4ft tank, 5ft better and of course 6ft and up even better.
You can never go wrong with more room for active fish like Tangs, or most fish for that matter.
With the exception of maybe the smaller Bristletooths, many Tangs seem to have a more linear and back and forth swimming style compared to the more zig-zag style of fish like angels.
FishBase lists their max size at 8”, 7” ones (IMO usually caught at or near that size) are considered “show size.”
The Tangs IMO that really need big, big tanks are mostly found in the genus Acanthurus, Naso and Paracanthurus (Dory). Sailfins too, they’re the giants among the Zebrasoma genus. Get big and very tall.
IMO 4ft 100-gallon (like the RSR 425- if I’m correct) would be a minimum.